In 1673, Jermyn was elected as a Member of Parliament for Bury St Edmunds in Suffolk.

He continued to oppose exclusion in subsequent votes, but he made no recorded speeches and was not appointed to any committees.

[1] Despite his opposition to exclusion, Jermyn was a supporter of the Glorious Revolution in 1688 and he signed the Association of 1696.

He died without male issue and was succeeded in his title by his brother, the former Jacobite, Henry Jermyn, 1st Baron Dover.

Jermyn's estate, valued at £15,000 per year, was divided among his four surviving adult daughters.